This invention is directed to an improvement in multi-terminal systems, and more particularly to a system in which a plurality of work stations share a large memory.
The recent rapid increase in the use of intelligent work stations, e.g., personal computers, has been accompanied by an increase in the demand for different techniques for interconnecting the work stations to make more efficient use of their collective resources. Some common interconnect schemes include ring-type and star-type local area networks. A significant advantage of such networks is not only the increased communication between stations but the more effective use of the collective data processing capacity of the terminals on the network.
One resource which lends itself quite well to a sharred arrangement is Random Access Memory (RAM). Random Access Memory capacity is a relatively expensive resource, and most work stations provide a relatively small amount of RAM in conjunction with a larger backing store, e.g., a disk storage. Constant storage and retrieval of data will typically require frequent disk accesses, thereby slowing down the overall data processing speed. On the other hand, providing any given work station with sufficient RAM to avoid frequent disk accesses would be prohibitively expensive and would often not be justified by the relatively few occasions on which such a large memory capacity would be needed. Thus, a significant savings in cost and increase in efficiency could be achieved by interconnecting a plurality of intelligent work stations to share a common memory, and the present invention is directed to an improvement in such a shared memory system.
In existing insertion-ring or broadcast-buss interconnect systems, local processing is encumbered by the local storage limitations at each work station, as described above, and it is an object of this invention to permit extended local processing unencumbered by local storage limitations, thereby providing a significant performace advantage over insertion-ring or broadcast-buss networks.
Interconnection of known networks with conventional data base systems is sometimes complex due to the distribution of control information throughout the system, and it is a further object of this invention to provide a memory-coupled network wherein the interface with conventional data base systems is simpler and more efficient due to centralization of the control information.
It is a still further object of this invention to provide a shared memory system in which the bandwidth of each switch connection for coupling a given intelligent work station to the shared memory is driven only at the speed of the microprocessor of that station, thereby providing a significant advantage over typical insertion-ring or broadcast-buss interconnect systems wherein the ring bandwidth is driven by the sum of all active work station microprocessors.